The present invention relates to an engine control equipment, particularly to a control equipment of a compressive self-ignition engine for accelerating activation of a catalyst.
A car engine has such main problems as improvement of fuel consumption and reduction of exhaust gas. A lean burn engine has recently become a mainstream, which uses a combustion system according spark ignition to improve the fuel consumption by operating an air-fuel ratio at a lean in order to reduce a pump loss.
However, though the spark-ignition-type lean burn engine can reduce the pump loss by making an air-fuel ratio leaner, there is a lean limit due to an ignition error according to the theory of the engine because the engine uses combustion according to flame spread.
However, there is a combustion-type engine according to the compressive self-ignition of making a fuel-air mixture spontaneously ignite in a combustion chamber instead of using the spark ignition by a spark plug. The compressive-self-ignition engine causes a combustion reaction everywhere in the combustion chamber. Therefore, it is possible to improve the fuel consumption and thereby reduce NOx because the engine has a lean limit higher than that of the spark-ignition type and moreover, there is no local high-temperature portion and the combustion temperature is low.
Moreover, in the case of a usual engine, it is generally performed to make an exhaust pipe of the engine oxidize hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gas discharged from a combustion chamber and set a three-way catalyst having a function for reducing an nitrogen oxide (NOx). In the case of the three-way catalyst, the NOx reducing function of the three-way catalyst hardly functions in a lean operation as shown by the purifying performance of three components of a three-way catalyst to the air-fuel ratio in FIG. 34. Therefore, an NOx catalyst may be set which occludes or adsorbs NOx.
In the case of a compressive-self-ignition-combustion-type engine, it is necessary to greatly increase the combustion chamber in pressure and temperature. Therefore, various arts about an engine control equipment for changing the spark ignition type and the compressive self-ignition type in accordance with an engine operating condition in which spark ignition using a spark plug is performed when warming-up of the engine is not completed and the compressive self-ignition combustion is performed in the cases other than the above case or the compressive self-ignition combustion is performed when the compressive self-ignition combustion can be made and an ignition timing can be properly obtained are disclosed (refer to official gazettes of Japanese Patent Laid-Open Nos. 157220/1987, 6435/1999, 336600/1999, 62589/1999, 257108/1999, 166435/1999, and 294152/1999).
Moreover, by considering that the purifying performance of an exhaust gas by a three-way catalyst is lowered when an engine is cooled, various arts of an engine control equipment for accelerating activation of the catalyst are disclosed (refer to official gazettes of Japanese Patent Laid-Open Nos. 45844/2000 and 336574/1999).
As shown in FIG. 35, the above three-way catalyst shows HC, CO, and NOx purifying functions when an exhaust gas has a predetermined temperature or higher. However, the catalyst has a characteristic that it cannot completely purify the exhaust gas when the exhaust gas has a temperature lower than the predetermined temperature. Therefore, it is necessary to keep the exhaust gas at a predetermined temperature or higher in order to maintain the above activated state. That is, as shown in FIG. 36, in the case of the three-way catalyst set to the exhaust pipe, the exhaust-gas purifying performance of the catalyst is deteriorated in the period from the time when an engine is started until the time when an exhaust gas reaches a predetermined temperature or higher. This is because the engine has the temperature equal to the then outside-air temperature when it is started and the temperature of its exhaust gas is also low, and the catalyst is activated after it is heated by the exhaust gas.
Therefore, when setting a catalyst to the exhaust pipe, it is necessary to shorten the time from start of an engine up to activation of the catalyst, that is, any means for activating the catalyst is necessary.
The above mentioned is particularly necessary for a combustion-type engine according to compressive self-ignition. The is because in the case of the combustion type according to compressive self-ignition, the combustion temperature is lower than the case of the spark ignition type and thereby, the effect of raising the temperature of a catalyst by heating an exhaust gas is small. Therefore, exhaust-gas deterioration becomes a large problem at start of the engine.
That is, the present inventor obtains the new knowledge that when setting a catalyst to the exhaust pipe of a combustion-type engine according to compressive self-ignition, it is possible to shorten the time from start of the engine up to activation of the catalyst and therefore, it is possible to prevent exhaust-gas deterioration also in the case of the combustion type according to compressive self-ignition.
However, though the above prior art has means for changing the spark-ignition type and the compressive self-ignition type, the engine control equipments disclosed in the official gazettes of Japanese Patent Laid-Open Nos. 157220/1987 and 6435/1999 notice only a combustion state, determine directly or indirectly whether the combustion state allows compressive self-ignition, and permit the combustion by compressive self-ignition when the combustion state allows the compressive self-ignition. Therefore, when combustion by compressive self-ignition can be made even if a catalyst is inactivated, compressive self-ignition combustion may be performed. Moreover, other prior arts do not particularly consider activating a catalyst in order to early perform the combustion by compressive self-ignition though they respectively control the opening/closing timing of an intake or exhaust valve in accordance with the operation state or heat a catalyst in order to reduce smoke and NOx at the same time.
The present invention is made to solve the above problems and its object is to provide an engine control equipment capable of preventing an exhaust gas from deteriorating by activating a catalyst in order to early perform the combustion by compressive self-ignition.
To achieve the above object, an engine control equipment of the present invention is an engine control equipment basically having a catalyst for burning a mixed gas in a combustion chamber by compressive self-ignition and purifying exhaust-gas components in the combustion chamber. The control equipment is provided with means for controlling the catalyst and the means for controlling the catalyst is provided with means for determining the activated state of the catalyst and means for activating the catalyst in accordance with a determination result of the means for determining the activated state of the catalyst.
In the case of the engine control equipment of the present invention constituted as described above, the means for activating a catalyst accelerates the activation of the catalyst in accordance with a determination result of a catalyst state. Therefore, it is possible to shorten the time from start of an engine up to activation of a catalyst, prevent an exhaust gas for activating the catalyst from deteriorating, and improve the reliability of the engine.
Moreover, in the case of a specific mode of an engine control equipment of the present invention, the means for determining the activated state of the catalyst is provided with means for detecting or estimating the temperature of the catalyst and means for determining the activation of the catalyst. The means for activating the catalyst controls the operation state of an engine when the detected or estimated temperature of the catalyst is equal to or lower than a predetermined value.
In the case of another mode of the engine control equipment of the present invention, the means for activating the catalyst inhibits the combustion by the compressive self-ignition and performs the combustion by spark ignition when the detected or estimated temperature of the catalyst is equal to or lower than a predetermined value.
In the case of still another mode of the engine control equipment of the present invention, the means for activating the catalyst drives a heater for the catalyst when the detected or estimated temperature of the catalyst is equal to or lower than a predetermined value.
In the case of still another mode of the engine control equipment of the present invention, the means for activating the catalyst injects a fuel at the timing other than usual fuel injection when the detected or estimated temperature of the catalyst is equal to or lower than the predetermined value and the fuel injection timing coincides with the explosion or exhaust stroke of the engine.
Moreover, an engine control equipment of the present invention is controlled so as to early perform the combustion by the compressive self-ignition when a temperature detected by a temperature sensor provided for the upstream or downstream side of the above catalyst shows a predetermined value or higher and the catalyst uses a three-way catalyst or NOx catalyst set to an exhaust pipe.